Acoustic transmission is one method of underwater communications. Commercial off-the-shelf acoustic modems are available. However, many underwater communications applications require non-acoustic transmission, such as applications with operational constraints on sonar interference, security constraints of being overheard, and technical interests in signal speed, bandwidth, device scale and power. Even as acoustic technologies mature, the physical principles of optical signal propagation and scattering in water are fundamentally faster (1500 meters per second for acoustic signal propagation underwater compared to 108 meters per second for electromagnetics) and more rapidly modulated (up to of 100 kilobaud for acoustics compared to many Gigabaud for electromagnetics).